1. Field of the Invention
The present invention relates to a seat reclining apparatus.
2. Description of Related Art
A seat reclining apparatus in which a base plate and a ratchet plate (ratchet) which are rotatable relative to each other about a relative rotation axis are fixed to one and the other of a seat cushion side frame and a seatback side frame, respectively, is known in the art as a seat reclining apparatus installed onto a vehicle seat. An internal gear which is centered about the relative rotational axis is formed on the ratchet plate, and a plurality of radial guide grooves are formed on the base plate. A plurality of lock members, each of which has an outer toothed portion engageable with the internal gear of the ratchet plate, are movably supported by the plurality of guide grooves therein. By operating an operating mechanism (cam mechanism), each of the plurality of lock members moves between an engaged position in which the outer toothed portion is engaged with the internal gear and a disengaged position in which the outer toothed portion is disengaged from the internal gear to allow the seatback to be fixed at an arbitrary position within a seating position (range). This structure is disclosed in Japanese Unexamined Patent Publication No. 2012-61096.
In this seat reclining apparatus, a certain amount of play in a circumferential direction (circumferential play) between each lock member and the associated guide groove of the base plate cannot be avoided. When the seat reclining apparatus is locked, the outer toothed portion of each lock member is engaged with the internal gear of the ratchet plate, so that, in a strict sense, play also exists between the internal gear of the ratchet and the outer toothed portion of each lock member; however, this circumferential play between the internal gear of the ratchet plate and the outer toothed portion of each lock member is far smaller than circumferential play of each lock member relative to the associated guide groove, and from the viewpoint of play when the seatback is locked, the effect of circumferential play of each lock member relative to the associated guide groove is far greater than that between the internal gear of the ratchet plate and the outer toothed portion of each lock member. Although play about the relative rotation axis between the base plate and the ratchet plate also exits in the seatback, here the issue of play occurring in the seatback relative to the seat cushion is considered, which is caused by circumferential play of each lock member relative to the associated guide groove, and no issue is made out of play occurring in the seatback relative to the seat cushion which is caused by play about the aforementioned relative rotation axis.
On the other hand, if circumferential play in all of the lock members, which are movably supported by the base plate, is strictly controlled, since all the lock members are pressed against guide surfaces of the corresponding guide grooves in a state where the seat reclining apparatus is locked, each lock member is immovable in the circumferential direction of the base plate relative to the base plate (the associated guide groove). However, if circumferential movement of each lock member is controlled in such a manner, the outer toothed portion of any lock member may become incapable of being engaged with the internal gear of the ratchet plate due to variations in the shapes of the lock members and the guide grooves (due to manufacturing error).